1. Field of the Invention
The present invention relates to a process for preparing thermoplastically processible starch polymer mixtures or starch derivative mixtures according to the preamble of claim 1 and to a number of uses.
The present invention in particular relates to thermoplastically processible transesterification products of starch or derivatives thereof with, for example, lactones, esteramides, fatty acids, etc. and/or polyesters or other biologically degradable hydrophobic polymers and mixtures of transesterification products with the above-mentioned polymers. Their use is based on the fact that numerous types of starch, as macromolecular raw materials, are cheaper than the known thermoplastic materials.
Additionally, the present invention relates to processes for preparing the transesterification products of starch or derivatives, such as, in particular, starch acetates.
2. The Relevant Technology
Thermoplastically processible blends of starch have been described in WO 90/05161. Thermoplastically processible blends of starch, of softeners and of water-insoluble polymers display only limited uptake of water and have useful mechanical strength, but they are not storable at any level of surrounding humidity in the long term.
In addition, in JP 05 125 101, transesterification products of starch have been described which melt in the temperature range of from 150 to 170.degree. C.; however, these products are unsuitable for wide use owing to their water uptake from the surrounding air and their poor mechanical properties. The preparation of these products by the known processes is prohibitive for wide use.